Hard disk drives are used in almost all computer system operations, and recently even in consumer electronic devices such as digital cameras, video recorders, and audio (MP3) players. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model was established approximately 50 years ago. The hard drive model includes a plurality of storage disks or hard disks vertically aligned about a central core that can spin at a wide range of standard rotational speeds depending on the computing application in which the hard disk drive is being used. Commonly, the central core is comprised, in part, of a spindle motor for providing rotation of the hard disks at a defined rotational speed. A plurality of magnetic read/write transducer heads, commonly one read/write transducer head per surface of a disk, where a head reads data from and writes data to a surface of a disk, are mounted on actuator arms.
Data is formatted as written magnetic transitions (information bits) on data tracks evenly spaced at known intervals across the disk. An actuator arm is utilized to reach out over the disk to or from a location on the disk where information is stored. The complete assembly at the extreme of the actuator arm, e.g., the suspension and magnetic read/write transducer head, is known as a head gimbal assembly (HGA).
In operation, pluralities of hard disks are rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are channels or tracks evenly spaced at known intervals across the disks. When a request for a read of a specific portion or track is received, the hard disk drive aligns a head, via the actuator arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk drive aligns a head, via the actuator arm, over the specific track location and the head writes the information to the disk.
To enable the read/write head to be properly oriented above the target track, there is disposed on the hard disk information that provides for correctly directing the read/write head to the specific track location. Each track is divided into a number of data sectors and servo sectors. The data sectors are used to contain user data and the servo sectors contain the information for properly locating the read/write head. Due to advances in electronic and manufacturing technologies, there has been a constant increase in the areal density of a hard disk, and while providing an increase in the amount of data that can be stored upon a hard disk, those advancements have proportionally decreased the physical size of the sectors and the tracks therewithin. As track size decreases, there is an increased possibility of data read and/or data write errors which can be caused by track misreading, track mis-registration, mis-alignment of the read/write head, and/or other errors that can cause a read/write error and/or failure. Accordingly, it is becoming more critical to the proper operation or the read/write head to have the information for directing the read/write head precisely and correctly disposed upon the hard disk.
Particularly, prior to hard disk drive assembly, there is a process of servo track writing (STW) in which a manufacturer of a hard disk drive disposes upon the hard disk the positioning information used to locate the read/write head over a given track of the hard disk.
In servo track writing, there are inherent problems in assuring proper (servo track writing) STW. For example, high-frequency repeatable run out (RRO) track mis-registration (TMR) harmonics are present, which can be a major performance detractor to the programming or servo writing to the hard disk. A primary cause of the high-frequency RRO TMR harmonics is the forcing mechanism driven by motor excitation during STW. Another primary cause of the high-frequency RRO TMR harmonics is the associated mechanical system modes having natural frequencies that approximate the excitation frequencies. This results in the written-in RRO TMR that is induced during the STW manufacturing process.
One solution to reduce the written-in RRO TMR was to utilize a written-in servo feed forward method. In this particular method, prerecorded servo RRO feed forward information is utilized and which is written during the STW process on a dedicated servo disc or on servos angularly spaced. The written feed forward information is then read from a servo sector and then used to compensate head positioning for the next servo sector.
This solution is not without certain shortcomings. One such shortcoming of using the servo feed forward method is the significant amount of time that is required during the hard disk drive STW manufacturing process. Another shortcoming is the requirement of additional space on the hard disk that is utilized to store the RRO feed forward information, which can detrimentally affect the storage capacity of the hard disk. Yet another shortcoming is the requirement of additional product speed servo overhead timing in order to read the RRO feed forward information at each servo sector.
Another solution to reduce the written-in RRO TMR is to pre-write or print the servo information onto the hard disk prior to placing the disk(s) into the disk-spindle assembly. The servo information can include RRO feed forward cancellation values. This pre-writing or printing is similar to techniques utilized in the manufacturing of compact discs, e.g., CDs, or digital versatile discs, e.g., DVDs.
This solution is also not without certain shortcomings. One shortcoming is the additional time that is required to accomplish the disk drive servo track writing manufacturing process, which can inherently reduce yield per fix time. Another shortcoming is the requirement of additional disk space to store the RRO feed forward information, which can have a detrimental affect on disk storage capacity. Yet another shortcoming is the requirement of additional product speed servo overhead timing in order to read the RRO feed forward information at each servo sector. Still another shortcoming is that the thermal condition during manufacturing may differ from that of the user. This could cause improper calibration of the correct information because of disk deformation and/or environmental conditions, e.g., temperature. In this particular situation, the servo may utilize incorrect values to correct the target RRO harmonics.
Yet another solution to reduce the written-in RRO TMR is to redesign the actuator or spindle related components for reducing dynamic interaction between the mechanical components of the hard disk drive and the STW (servo track writer) during the servo track writing process.
However, this solution is also not without shortcomings. One shortcoming is the significant time that is required to accomplish the redesigning of the actuator or spindle related components. This can also negatively impact manufacturing tooling which is directly related to product development costs.
Therefore, a need exists for a method and system for servo track writing (STW) which reduces high amplitude RRO TMR harmonics while utilizing existing hard disk drive mechanical designs and hard disk drive manufacturing line tooling.